No one wants to spend his or her retirement years scrimping just to get by. The best way to avoid such a fate is to begin socking away money for retirement now and investing that money in assets that deliver excellent long-term returns.

You can cross bonds, CDs, and money market accounts off the list right out of the gate. While these can be relatively safe places to park some money, they won't give you the level of gains that you'll need to amass a comfortable retirement nest egg.

If you want to really be set for retirement, the best place to invest your money is in solid growth stocks. Three growth stocks that should help you retire rich are Guardant Health (GH -4.50%), MongoDB (MDB -1.69%), and The Trade Desk (TTD -2.95%).

Smiling man holding his hands up as money rains down from the sky

Image source: Getty Images.

1. Guardant Health

Guardant Health's shares skyrocketed nearly 108% higher in 2019. This tremendous gain should be just the beginning for the diagnostics company's growth story.

Two products have fueled Guardant Health's meteoric rise -- Guardant360 and GuardantOmni. Both are liquid biopsies that detect DNA fragments in the blood that have broken off from tumor cells. Guardant360 is used to match cancer patients with the most effective treatment option. Biopharmaceutical companies use GuardantOmni to screen prospective patients for clinical trials evaluating cancer drugs.

Look for Guardant360 and GuardantOmni to accelerate their already-strong sales momentum in 2020 and beyond. Guardant Health thinks that Guardant360 by itself could eventually generate annual sales of around $6 billion.

But the company has an even greater opportunity with its Lunar liquid biopsy assays that are currently available for research use only. Lunar-1 is designed to be used for recurrence monitoring of cancer in patients while Lunar-2 targets early cancer detection. The two products together could address an annual market of more than $45 billion. With Guardant Health's market cap at close to $8 billion right now, this stock should have tremendous upside potential.

2. MongoDB

MongoDB's name tells the company's story in a nutshell. Mongo is short for "humongous." DB, of course, stands for database. And MongoDB's powerful database platform gives the company a humongous growth opportunity.

Sure, databases have been around for decades. The problem, though, is that these databases weren't designed for today's world of unstructured data. They were also created to run in on-premises data centers, while in the 2020s everything is moving to the cloud. MongoDB's open-source database platform, on the other hand, was built from the ground up to handle any kind of data, including unstructured data, and to be run anywhere, including the cloud.

It's not surprising that MongoDB's revenue soared 52% year over year in the third quarter of 2019. Although the company still isn't profitable, it's just a matter of time before the profits begin pouring in.

MongoDB's future looks very bright. The already-huge global database market is growing. Mongo's market share is increasing faster than its major rivals. Its Atlas cloud-based fully managed database management product continues to enjoy exceptionally strong momentum. MongoDB stock jumped 57% in 2019 and has already vaulted over 35% higher so far in 2020. More big gains should be on the way over the long run.

3. The Trade Desk

The Trade Desk was the biggest winner among these great growth stocks last year, with its shares zooming nearly 124% higher. There are two trends powering the company's rise: (1) the shift to digital advertising, and (2) the shift to programmatic ad buying. Simply put, The Trade Desk's platform is paving the way for the future of advertising. 

You can just look around throughout the day to see how advertising is going digital. Websites, social media, and many streaming TV services incorporate ads that target specific audiences. And there are way too many advertising opportunities now for the back-and-forth negotiations used in the past to buy and sell ads to be effective. Programmatic advertising addresses this by using software to bid on and buy ads in ways that optimize advertising budgets.

At this point, only a small fraction of the buying and selling in the total global advertising market is done programmatically. But that's going to change. It seems like a safe bet that in the future practically all advertising will be digital and be transacted programmatically.

The Trade Desk is already very profitable. Its revenue continues to grow rapidly. The company should benefit in the near term from the explosive growth of connected TV and its efforts to move into more international markets and stands to prosper over the long term from the shift to digital and programmatic advertising. With a market cap of around $14 billion, The Trade Desk should have plenty of room to run and help you retire rich.